Curved solar panel mirrors have been long known. For instance, U.S. Pat. No. 4,124,277 discloses a concave mirror construction and a method of making concave mirrors, particularly of large focal length. A normally flat rigid glass mirror is held in a concave configuration under bending stress within its elastic limit by a holding layer of substantially dimensionally stable material bonded thereto. The holding layer is formed by a layer of open-ended expansible cellular material sandwiched between layers of pliable and solidifiable dimensionally stable material. The holding layer is bonded to the glass mirror while the mirror is being mechanically held in a concave configuration under bending stress within its elastic limit. The holding layer is cured in situ to a solid and dimensionally stable state which holds the glass mirror in the concave configuration.
Furthermore, U.S. Pat. No. 7,077,532 discloses a solar collector comprising a glass mirror, and a composite panel, wherein the back of the mirror is affixed to a front surface of the composite panel. The composite panel comprises a front sheet affixed to a surface of a core material, preferably a core material comprising a honeycomb structure, and a back sheet affixed to an opposite surface of the core material. The invention may further comprise a sealing strip, preferably comprising EPDM, positioned between the glass mirror and the front surface of the composite panel. The front sheet and back sheet are preferably made of carbon steel.
Moreover, U.S. Pat. No. 4,238,265 discloses a method for producing curved glass solar collectors. The method includes the following steps: (1) a microsheet of glass is drawn from a glass melt; (2) a reflective layer, such as silver, is deposited on one surface of the microsheet; (3) a first flexible backing layer, such as fiberglass, is bonded to the reflective layer; (4) the combination of the microsheet with the reflective layer and the first backing layer is formed over a mandrel which is preferably in the form of a parabolic cylinder; and (5) a honeycombed layer, with a second fiberglass backing layer, is then bonded to the first backing layer. The product produced by the steps 1-5 is then cured so that it retains the desired configuration, i.e. parabolic-cylindrical, after it is removed from the mandrel.
Another production method is disclosed in U.S. Pat. No. 4,422,893, which discloses a method of manufacturing a mirror which comprises the steps of selecting a former of shape complementary to the shape of the desired mirror surface, applying to such former a plurality of mirror elements each constituted by a glass element having a reflective coating on one face thereof, and applying and adhesively bonding directly to such mirror elements a preformed, substantially rigid, unitary structural support. The mirrors disclosed have an outer glass layer which is coated by a metal, such as aluminium or silver, an adhesive layer, such as comprising glue or silicone, and a sheet of expandable glass. According to one embodiment, there is shown a glass layer coated with silver which is bonded by a glue layer of polyester to a honeycomb structure cellular support.
Furthermore, EP1397621 discloses sun reflecting panels which have a sandwich structure having a reflecting surface made of glass, a honeycomb central core of aluminium and two thin outer skins of a high resistance material, where either said outer skins are made of steel or aluminium and where a further layer of glass fibres is inserted between the concave side of the aluminium skin and the thin reflecting mirror, such an arrangement obviating the great differences existing between the thermal expansion coefficient of the mirror and that of the aluminium skin.
One aim of the present invention is to provide an optimal curved solar panel mirror unit which renders high precision and as such also gives low losses when used in a solar panel, and which mirror unit also is cost-effective in comparison with other high-precision panel mirror units. Furthermore, one other purpose of the present invention is to provide a solar panel mirror unit which is very cost-effective in relation to the obtained yield when being used in a solar panel, i.e. which is relatively inexpensive to produce but still gives high precision, regardless of when solar energy is possible to generate.